1. Field of the Invention
This invention relates to a catalyst component used for producing highly crystalline olefin polymers and a process for producing the same. More particularly it relates to a catalyst component for producing highly crystalline olefin polymers from which a film having a superior transparency and very few voids is afforded, and a process for producing the same.
2. Description of the Related Art
It has been well known that crystalline olefin polymers such as crystalline polypropylene, etc. are obtained by polymerizing olefins by means of the so-called Ziegler-Natta catalyst comprising a compound of a transition metal of Groups IV to VI of the Periodic Table and an organometal compound of a metal of Groups I to III of the Table. As the transition metal compound catalyst component, various titanium trichloride compositions have been particularly broadly used.
Among these titanium trichloride compositions, those of a type obtained by reducing TiCl.sub.4 with an organoaluminum compound, followed by heat treatment, afford a polymer having a good form; thus many improved processes for producing the above type compositions have been researched. For example, a process of reducing TiCl.sub.4 with an organoaluminum compound, followed by treating the resulting titanium trichloride with an electron donor and TiCl.sub.4 to thereby enhance the catalyst activity and reduce the quantity of amorphous polymers formed (Japanese patent publication No. Sho 53-3,356/1978) and the like processes have been disclosed.
The present inventors have already proposed a number of processes in this field. According to the following processes among the above, the storage stability of titanium trichloride compositions, the polymerization activity, the crystallinity of the resulting olefin polymers, etc. have been notably improved as compared with those of conventional processes:
A process of producing olefin polymers using a titanium trichloride composition obtained by-reacting TiCl.sub.4 with a reaction product of an organoaluminum compound with an electron donor, followed by reacting the resulting solids with an electron donor and an electron acceptor (Japanese patent publication No. Sho 59-28,573/1984), and
A process of producing olefin polymers using a titanium trichloride composition obtained by reacting TiCl.sub.4 with a reaction product of an organoaluminum compound with an electron donor, followed by subjecting the resulting solids to polymerization treatment with an olefin and reacting the resulting material with an electron donor and an electron acceptor (Japanese patent application laid-open No. Sho 58-17,104/1983).
Further, on the other hand, in recent years, there has been energetically researched a process for producing olefin polymers which comprises using a titanium-containing solid catalyst component containing Ti, Mg, a halogen and an electron donor, which component exhibits a very high polymerization activity while retaining a high stereo-regularity, and polymerizing olefins in the presence of a catalyst obtained by combining the above solid catalyst component, an organoaluminum compound and an electron donor together (e.g. Japanese patent application laid-open No. Sho 58-83,006/1983, etc.).
The present inventors have also already proposed a number of processes. For example, we have disclosed processes for producing olefin polymers having a high stereoregularity and a good particle form with a high polymerization activity (e.g. Japanese patent application laid-open Nos. Sho 61-209,207/1986, Sho 62-104,810/1987, Sho 62-104,811/1987, Sho 62-104,812/1987, Sho 62-104,813/1987, etc.).
However, while these improved processes are provided with the above-mentioned advantages, films prepared from the resulting polyolefins are translucent so that the commodity value is often damaged depending on the fields of use applications; thus improvement in the transparency has been desired.
On the other hand, improvement in the transparency of films prepared from olefin polymers has been attempted. For example, processes of adding a nucleating agent such as aluminum salts of aromatic carboxylic acids (Japanese patent publication No. Sho 40-1,652/1965), benzylidene sorbitol derivatives (Japanese patent application laid-open No. Sho 51-22,740/1976), etc. to polypropylene have been proposed. However, when aluminum salts of aromatic carboxylic acids are used, their dispersibility in the resulting polymer is not only inferior, but also the effectiveness of improvement in the transparency of the resulting film is insufficient, while when benzylidene sorbitol derivatives are used, a definite improvement in the transparency is observed, but there have been raised problems that their smell at the time of processing is strong, a bleeding phenomenon(exudation) occurs, etc.
For solving the above-mentioned problem at the time of addition of nucleating agents, there have been proposed processes of polymerizing propylene using a catalyst obtained by polymerizing a small quantity of vinylcyclohexane, p-t-butylstyrene, allyltrimethylsilane, 4,4-dimethylpentene-1, etc., followed by preactivation treatment (Japanese patent application laid-open Nos. Sho 60-139,710/1985, Sho 63-15,803/1988, Sho 63-15,804/1988, Sho 63-218,709/1988, etc.). The present inventors produced polypropylene according to the proposed processes, and as a result found that in any of the processes, the polymerization activity of propylene not only lowered, but also there occurred operational problems such as formation of bulk polymer, scale adhesion onto the wall of polymerization vessel, inferior controllability of polymerization reaction, etc. Thus these processes could not be employed in the case of commercial, long term, continuous polymerization, particularly in the case of gas phase polymerization process wherein olefin polymerization was carried out.
Further, when the resulting polypropylene was processed into film, a definite improvement in the transparency was observed, but a large number of voids occurred in the film to thereby damage the commodity value.
Further, as a similar technique, there has been proposed a process of polymerizing propylene using a transition metal catalyst component having vinylcyclohexane polymer, allyltrimethylsilane polymer, etc. added in advance midway during the preparation of the component (Japanese patent application laid-open No. Sho 63-69,809/1988). However, since the proposed process requires a separate step of preparing the vinylcyclohexane polymer, allyltrimethylsilane polymer, etc., commercial disadvantage is not only brought about, but also there has been raised the above-mentioned problem that voids occur in the resulting film as observed in the prior art.
The present inventors have made extensive research on a transition metal catalyst component for producing olefin polymers, having overcome the above-mentioned problems of the prior art, that is, capable of producing crystalline olefin polymers stably and for a long term, and when made into film, affording a film having few voids and an improved transparency. As a result, we have found a titanium trichloride composition or a supported type titanium catalyst component, each having a linear olefin-non-linear olefin block compolymer contained therein according to a specified process, and further have found that when an olefin polymer is produced using a catalyst having at least an organoaluminum compound combined with the above titanium trichloride composition or the supported type titanium catalyst component, the above-mentioned problems of the prior art in the aspect of production and quality can be solved.